The present invention relates to a drive circuit for an electric motor used to e.g. generate an assist torque for a power steering, which can avoid various problems (such as malfunction and breakage) caused by heat from a semiconductor chip or chips. The present invention also relates to a method for assembling such a drive circuit.
Japanese Laid-Open Patent Publication No. 8-2430 discloses a drive circuit for an electric motor in a power steering. In this type of drive circuit, a radiator is provided separately from a circuit board in order to radiate heat from semiconductor chips and prevent chip packages sealing therein the semiconductor chips from thermally expanding. This makes it possible to prevent other circuit components from being adversely affected by the thermal expansion of the chip packages. However, the drive circuit has to be assembled by attaching the chip packages to the radiator so that the chip packages and the radiator are brought into intimate contact with each other, and then, soldering terminals of the semiconductor chips to the circuit board. The process for assembling the drive circuit is so complicated that the manufacturing cost of the drive circuit is increased.